The present invention relates to an image transfer material separation and transportation apparatus for an electrophotographic copying apparatus.
In electrophotographic copying systems of various types, known image transfer type electrophotographic copying systems are roughly classified into a visible image transfer type in which electrostatic latent images are formed on the surface of a photoconductor and the electrostatic latent images are developed into visible images, which are then transferred to an image transfer material; and an electrostatic latent image transfer type in which the electrostatic latent images formed on the surface of a photoconductor are transferred to an electrostatic latent image transfer material and the transferred electrostatic latent images are developed to visible images.
In either of the above-mentioned image transfer type electrophotographic copying systems, the image transfer material is transported in uniform contact with the surface of a photoconductor and the process of separating such image transfer material from the photoconductor after the image transfer process is a very important process. Various types of image transfer material separation and transportation apparatus with the above-mentioned function has been proposed and provided for practical use.
Furthermore, various types of photoconductors are also known for use in the electrophotographic copying apparatuses of the image transfer type, for instance, drum-shaped photoconductors and belt-shaped photoconductors. Hereinafter, for the convenience of explanation, only an electrophotographic copying apparatus employing a drum-shaped photoconductor (hereinafter referred to as "photo-conductor drum") will be explained.
Around the photoconductor drum, there are arranged a charging apparatus, an exposure optical system, a development apparatus, an image transfer apparatus, a sheet separation and transportation apparatus, a cleaning apparatus, a charge quenching apparatus and other known devices. The photoconductor drum is rotated in a predetermined direction and a visible image is formed on the surface of the photoconductor drum after the processes of charging, exposure and development. When the visible image formed on the photoconductor drum comes to an image transfer section, an image transfer material is brought into close contact with the surface of the photoconductor drum in synchronization with the arrival of the visible image at the image transfer section, so that the visible image formed on the surface of the photoconductor drum is transferred to the image transfer material by the image transfer apparatus.
The image transfer material to which the visible image has been transferred is separated from the surface of the photoconductor drum. As mentioned previously, various transfer material separation method are known, for instance, a method of employing a pick-off pawl is known. In that method, the image transfer material is separated from the surface of the photoconductor drum by a pick-up pawl which is in contact with the peripheral surface of the photoconductor drum. This method has a shortcoming in that the pick-off pawl may scratch the surface of the photoconductor drum. In another known transfer material separation method, air is jetted between the image transfer material and the peripheral surface of the photoconductor drum to separate the image transfer material from the surface of the photoconductor drum. This method has shortcoming in that noise is produced by the air jet, and developer particles and dust are significantly scattered within the copying apparatus by the air jet. In a further known transfer material separation method, a pick-off belt is disposed on the peripheral surface of the photoconductor drum at one end thereof on the downstream side with respect to the rotating direction of the photoconductor drum. In this method, after image transfer, the image transfer material runs onto the pick-off belt as it is transported. The image transfer material which has run on the pick-off belt is guided in such a direction that the image transfer material is separated from the surface of the photoconductor drum by a guide member which is attached to part of the pick-off belt.
In the image transfer sheet separation and transportation apparatus employing the above-mentioned pick-off belt, the side edges of the image transfer section are formed in such a manner that the image transfer sheet can be separated beforehand from the surface of the photoconductor drum by the pick-off belt. Therefore, the image transfer sheets can be securely separated from the photoconductor drum. In this sense, this is one of the excellent image transfer sheet separation and transportation apparatuses. However, that apparatus has an unavoidable drawback in that the image transfer cannot be done throughout the whole area including the longitudinal side portion of the image transfer sheet.
This drawback is unavoidable in the pick-off belt transfer material separation system, and when the image exists in the very side portion of the original document, part of the image in the side portion cannot be copied. Stated differently, the side edge portion is the so-called dead space, which is a big obstacle to increasing the effective image area on the photoconductor.